Tutedude offers best online courses with certificate after completing course and one time pay will give lifetime access
By kids, I am assuming the age group 4-15 years. Go for Laugh Guru, their courses are well explained and keeps the children glued to the course.
U can try coding blocks. They r teaching coding to small kids and it really should help in development of logical thinking and reasoning of the kid
There are lot of website and there app which will give excellent courses for your kids